Diffusion in polymerization

JL Duda. Molecular diffusion in polymeric systems. Pure Appl Chem 57 1681-1690, 1985. 

Gibson, C., Matthews, I. and Samuel, A., Microwave enhanced diffusion in polymeric materials, /. Microwave Power Electromagn. Energy, 1998, 23, 17. 

J. M. Zielinski and J. L. Duda, Solvent Diffusion in Polymeric Systems, in Polymer Devolatilization, R. J. Albalak, Ed., Marcel Decker, New York, 1996. 

The first attempts in the direction of simulating theoretically at an atomistic level the diffusion of simple gas molecules in a polymer matrix were made more than two decades ago (100). But, the systematic development of ab initio computer simulations of penetrant diffusion in polymeric systems dates only from the late 80 s (101-104). At the beginning of the 90 s it was achieved to simulate some qualitative aspects such as the diffusion mechanism, temperature, and pressure dependence of diffusion coefficients (105-109). The polymers chosen for investigation mainly fell into two categories either they were easily described (model elastomers or polyethylene) or they were known to have, for simple permanent gases like H2, 02, N2, H20 or CH4,... 

Photoisomerization was studied from a purely photochemical point of view in which photo-orientation effects can be disregarded. While this feature can be true in low viscosity solutions where photo-induced molecular orientation can be overcome by molecular rotational diffusion, in polymeric environments, especially in thin solid film configurations, spontaneous molecular mobility can be strongly hindered and photo-orientation effects arc appreciable. The theory that coupled photoisomerization and photo-orientation processes was also recently developed, based on the formalism of Legendre Polynomials, and more recent further theoretical developments have helped quantify coupled photoisomerization and photo-orientation processes in films of polymer. 

The bridge provides sufficient hydrophilicity and spatial mobility for the ligands to overcome both difficulties of ion diffusion in polymeric media, and steric inhibition of the polymer-bound ligands. The selectivity of the polymeric ligands obeys the Irving-Williams rule in the transition metal series. Separation of the element at the head of this series. Cu(ll) is thu.s readily obtained, provided iron is retained as Fe(II). Since the complexation is pH-dependent, this separation is most effective if carried out at the lowest possible pH (pH 2). The complexation phenomenon is completely reversible, and the rates of metal binding and release are reasonably fast. 

For diffusion in polymeric materials, a can be related to the polymer diffusivity of the sorbate... 

Overtone infrared spectroscopy described by Luck [3] is an effective means for determining quantitatively the concentrations of water in nonbonded and hydrogen bonded OH groups. Interesting results have been obtained for a variety of situations, including salt solutions, water-organic solvent mixtures, interface effects, organic molecule hydration, and diffusion in polymeric substrates. From such studies. Luck classifies water structure as (a) first shell water hydrate, (b) second shell, disturbed liquid-like water, and (c) liquid-like water. For salt transport in membranes, for diffusion of dyes in fibers, and for life in plant and animal cells, water of types b and c are essential. 

Behrens H, Nowak M (1997) The mechanisms of water diffusion in polymerized silicate melts. Contrib Mineral Petrol 126 377-385... 

The kinetic aspects of immobilized enzymes are rather complicated. A typical situation is when the enzyme is immobilized within some polymeric material, which may be cut into slices and immersed in a suitably buffered solution of the substrate. This is the type of situation that occurs in a biological system, an example being a muscle (in which the enzyme myosin is immobilized) surrounded by a solution of the substrate ATP. For reaction to occur, the substrate has to diffuse through the polymeric material in order to reach the enzyme. Reaction then occurs and the products must diffuse out into the free solution. Since diffusion in polymeric materia occurs more slowly than in water, there is now a greater possibility of diffusion control (see p. 403) the overall rate of reaction may depend to some extent on the rates with which these diffusion processes occur. 

Arizzi, S. Mott, P. H., and Suter, U. W. (1992) Space available to small diffusants in polymeric glasses - analysis of unoccupied space and its connectivity, J. Polymer Sci. Part B, 30, 415 26. 

Berens A (1977) Diffusion and relaxation in glassy polymer powders 1. Fiekian diffusion of vinyl chloride in poly(vinyl choride). Polymer 18(7) 697-704 Berens A, Hopfenberg H (1978) Diffusion and relaxation in glassy polymer powders 2. Separation of diffusion and relaxation parameters. Polymer 19(5) 489-496 Bond DA (2005) Moisture diffusion in a fiber-reinforced composite part 1 - non-Fickian transport and the effect of fiber spatial distribution. J Compos Mater 39(23) 2113-2141 Cai LW, Weitsman Y (1994) Non-Fickian moisture diffusion in polymeric composites. J Compos Mater 28(2) 130-154... 

Vibrational spectroscopy is perhaps the most frequently used technique for the study of diffusion in polymeric systems because it provides a rapid way to quantitatively describe this phenomenon. The two areas of this type of research include the diffusion of small molecules into polymers and polymer-polymer interdiffusion. The easiest and most commonly used technique for this purpose is ATR. In this experiment, a polymer film is placed in contact with an ATR crystal, and the diffusing species is placed on top of the polymer. As diffusion progresses, the diffusing species moves closer to the ATR crystal and shows up in the spectrum obtained as an increase in the diffusant specific spectral band. This spectral change can be used to determine the diffusion coefficient of the system with the appropriate diffusion equation. This technique is limited to IR because of the optics and sample geometry required. 

Kulkami, M. G. and Mashelkar, R. A., A unified approach to transport phenomena in polymeric media, I. Diffusion in polymeric solutions, gels and melts, Chem. Eng. Sci., 38, 925-939 (1983) II. Diffusion in solid structured polymers, Chem. Eng. ScL, 38, 941-953 (1983). 

Freeman, B. D. (1992). Mutual diffusion in polymeric systems. In S. L. Aggarwal and S. Russo (Eds.), Comprehensive Polymer Science First Supplement. Pergamorr, New Yrrrk p. 167. Freeman, B. D. (1999). Basis of permeabihty/selectivity tradeoff relations in polymeric gas separation membranes. Macromolecules 32, 375. 

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